1. Field of the Invention
This invention relates to autodeposition. Autodeposition involves the use of an aqueous resinous coating composition of relatively low solids concentration (usually less than about 10%) to form a coating of relatively high solids concentration (usually greater than about 10%) on a metallic surface immersed therein, with the coating increasing in thickness and areal density (mass per unit area of coating) the longer the time the metallic surface is immersed in the composition. Autodeposition is somewhat similar to electrodeposition but does not require the aid of external electrical current to cause the resin particles to deposit on the metal surface. In general, autodepositing compositions are aqueous acid solutions having solid resin particles dispersed therein in very finely divided form. The coating formed while the metal substrate used is immersed in the bath is generally wet and fairly weak, although sufficiently strong to maintain itself against gravity and moderate spraying forces. In this state the coating is described as "uncured". To make an autodeposition coated object suitable for normal practical use, the uncured coated is dried, usually with the aid of heat. The coating is then described as "cured".
The present invention relates more particularly to the chemical treatment of an uncured autodeposited coating for the purpose of improving various properties thereof, particularly the adhesion of the coating to the underlying metal substrate and the resistance to corrosion of the underlying metal provided by the cured autodeposited coating when the coated metal surfaced object is subjected to corrosive environments.